The present invention relates generally to spinal surgery, and more particularly to a method and apparatus for expanding a spinal canal to relieve pressure on spinal nerves.
Spinal Stenosis, or narrowing of the spinal canal, inflicts millions of people with back and leg pain due to compression of spinal nerves. Severe spinal stenosis often leads to surgery in an effort to relieve compressed nerves and lessen back and leg pain. Spinal laminectomy is the traditional operation performed to treat spinal stenosis. In the spinal laminectomy, posterior aspects of the spinal column are removed to xe2x80x9cun-roofxe2x80x9d the spinal canal to relieve the pressure on the nerves. Specifically, a spinous process, lamina and portions of various facet joints are the posterior aspects of the spinal column surgically excised.
Although the spinal laminectomy is often successful in relieving pressure on the nerves of the spinal canal, several problems and disadvantages arise as a result of the laminectomy. First, the laminectomy removes important sites of back muscle attachment leading to back muscle dysfunction and pain. Second, the laminectomy exposes the nerve sac causing scar tissue to form around the nerves. Scar tissue may prevent normal motion of the nerves, leading to recurrent pain. Third, the laminectomy can destabilize the spine resulting in a forward slippage of one vertebra on another. Vertebral slippage can cause recurrent pain and deformity. Fourth, the laminectomy requires a large surgical exposure and significant blood loss, making the laminectomy dangerous for older patients. Finally, spinal stenosis can recur following the laminectomy, requiring risky revision surgery.
Laminectomy risks have led surgeons to seek an alternative for patients with severe spinal stenosis. Some surgeons choose to treat spinal stenosis with multiple laminotomies. Laminotomies involve removing bone and soft tissue from the posterior aspect of the spine making xe2x80x9cwindowsxe2x80x9d into the spinal canal over areas of nerve compression. Multiple laminotomies remove less tissue than the laminectomy, resulting in less scaring, vertebral instability and blood loss.
Multiple laminotomies, however, also suffer from problems and disadvantages. Laminotomies may not adequately relieve nerve compression and the pain may continue. Laminotomies are more difficult to correctly perform than the laminectomy. Laminotomies expose the nerves and may cause nerve scaring. Patients receiving multiple laminotomies also often have recurrent spinal stenosis requiring risky revision surgery.
Zucherman, et. al., discloses another approach (differing from laminectomies, laminotomies and the present invention) to spinal stenosis in U.S. Pat. No. 5,836,948, where a device and method is described to distract (spread apart) spinous processes of adjacent vertebrae and prevent extension of the spine. While the Zucherman technique may help to relieve some spinal canal narrowing due to in folding of posterior soft tissues, the bony spinal canal remains unchanged in size. Without expanding the spinal canal area, the Zucherman technique offers limited benefit for spinal stenosis sufferers. Furthermore, arthritic facet spurs, the main cause of degenerative spinal stenosis, remain unaffected by the Zucherman approach and continue to cause pain. Also, the distraction of the spinous processes as described by Zucherman creates a forward curvature of the spine called kyphosis. Lumbar kyphosis is a spinal deformity often associated with back pain and dysfunction.
Information relevant to a wide variety of spinal implants including screw and rod constructs are described by Biedermann et. al. in U.S. Pat. No. 5,725,527, Tsou in U.S. Pat. No. 5,176,678, Kambin in U.S. Pat. No. 5,480,440 and Mathews in U.S. Pat. No. 5,496,322. These implants are useful for stabilizing the spine and the correcting spinal deformities, however, these references are not capable of expanding the spinal canal or treating spinal stenosis. Other implants operating as intervertebral spacers are described by Errico et. al in U.S. Pat. No. 5,653,763 and Kuslich in U.S. Pat. No. 5,059,13. These implants are useful in expanding the intervertebral disc space and assisting with spinal fusion, however, these references are also not capable of expanding the spinal canal or treating spinal stenosis.
For the foregoing reasons, there is a strong need for a different and better method for relieving the symptoms of spinal stenosis without the drawbacks of currently available techniques. A method is needed that expands the spinal canal, relieving pressure on the spinal nerves, while being simple, safe and permanent.
The present invention provides a simple, safe and permanent method and apparatus for treating spinal stenosis by expanding the spinal canal area to provide additional space for the spinal nerves, relieving pressure on the spinal nerves.
An object of the present invention is to maintain the integrity of the spinal canal so that the function of normal tissues is not destroyed or significantly altered as with a larninectomy and laminotomy.
Another object of the present invention is to avoid scarring around the spinal nerves by avoiding an open exposure of the nerves.
Another object of the present invention is to avoid causing spinal instability, where one vertebra slips forward on another vertebra causing recurrent pain and deformity.
Yet another object of the present invention is to decompress the spinal nerves with a quick, safe approach resulting in minimal blood loss.
Yet another object of the present invention is to provide a permanent solution to spinal stenosis, where no tendency exists for recurrence.
In one aspect of the present invention, a method for correcting spinal stenosis is introduced where a spinal canal is enlarged by cutting a vertebra, separating the vertebral cut and then stabilizing the cut, allowing the vertebra to heal with the spinal canal expanded, permanently creating more space for the spinal nerves thus relieving compression on the nerves.
In another aspect of the present invention, the method of expanding the spinal canal begins with cutting a vertebra (performing an osteotomy) at each spinal pedicle of the vertebra in an oblique fashion, beginning at a base of a transverse process of the vertebra and coursing medially and anteriorly at approximately a 45-degree angle to complete the cut through a medial wall of the pedicle to the spinal canal. Each osteotomy (bone cut) is then distracted (expanded) by inserting an implant into the osteotomy, increasing the diameter (and thus the area) of the spinal canal. The implant is stabilized, securing the osteotomies and the vertebra with the spinal canal in an expanded state.
In another aspect of the present invention, the implant comprises a stent and a screw. The stent is inserted into the vertebral cut, expanding the spinal canal. The screw is inserted through the stent and threaded into the vertebra, securing the stent, the vertebral cut and the expanded spinal canal.
In another aspect of the present invention, the implant comprises two stents and two screws. Each stent is inserted into one of two vertebral cuts, each stent insertion expanding the spinal canal. Each screw is inserted through one stent and threaded into the vertebra, securing the stent, the vertebral cut and the expanded spinal canal.
In another aspect of the present invention, the implant includes two stents, two screws, two washers and a cable. Each stent is inserted into one of two vertebral cuts, each stent insertion expanding the spinal canal. Each screw is inserted through one washer and one stent. Each screw is then threaded into an anterior portion of the vertebra, securing the washer, the stent, the vertebral cut and the expanded spinal canal. Each washer is connected to one of two ends of the cable, the cable being strapped around or through a posterior portion of the vertebra, securing the posterior portion of the vertebra to the anterior portion of the vertebra.
In another aspect of the present invention, the screw can include self-tapping, bone gripping threads. The screw can also include a rounded head.
In another aspect of the present invention, the stent is designed to accommodate the insertion of bone graft material to facilitate healing of the vertebra with expanded spinal canal. The stent can be U-shaped for this purpose. The stent can include a rounded, wedge-shaped end for ease in penetrating and separating the vertebral cut. The stent can include a flange designed to prevent the stent from penetrating into the spinal canal. The stent can also include a rounded depression adapted to rotatably accept a rounded washer and/or a rounded head on the screw for securing the stent to the vertebra.
In another aspect of the present invention, the washer can include a rounded shape substantially similar to and engagable with a rounded head on the screw and a rounded depression in the stent. The rounded head of the screw would reside within the rounded washer and both would be rotatably housed within the rounded depression in the stent.
The present invention has the following advantages over current, unrelated techniques for treating spinal stenosis:
(1) Normal spine structures are not removed and thus normal muscle attachments are maintained.
(2) There is less chance of spinal instability.
(3) There is less manipulation of the spinal nerves.
(4) There is less scaring around the spinal nerves.
(5) Spinal decompression is more complete.
(6) The operation is quicker and safer with less blood loss.
(7) The expanded spinal canal is permanent, preventing recurrent spinal stenosis.